Method of molding reflector devices



Feb. 21, 1950 J. c. HAGGART, JR

METHOD OF MOLDING REFLECTOR DEVICES 3 Shets-Sheet 1 Original Filed 00L3, 1947 INVENTOR 7 f/ayyar'ljJr: BY

ATTORNEY Feb. 21, 1950 J. c. HAGGART, JR 2,498,489

METHOD OF MOLDING REFLECTOR DEVICES Original Filed Oct. 3, 1947 3Sheets-Sheet 2 INVENTOR ATTORNEY Patented Feb. 21, 1950 METHOD OFMOLDING REFLECTOR, DEVICES John C. Haggart, Jr., Los Angeles, Calif.

Original application October 3, 1947, Serial No. 7 77,693. Divided andthis application February 10, 1948, Serial No. 7,315

3 Claims.

This application is a division of application Serial No. 777,693, filedOctober 3, 1947, now Patent No. 2,479,350.

The invention relates to the forming of reflector units of the typewhich within a considerable angle of incidence will return incidentlight substantially in the direction of incidence. Such units arevariously referred to as retro-directive and as auto-collimating units.Functionally and structurally they fall into the two categories ofcentral triple reflector units and lens-reflector units.. It is withunits of the latter category that this invention has especial utility.

More particularly, this invention has application to the problems thatarise in connection with the forming of disc units, that is, membersthat resemble discs, in that their thickness is considerably less thantheir other dimensions and they are composed of a plurality ofcontiguous small reflective elements, the eiiect of which at anysubstantial distance is to integrate the individual luminous areas intoone composite luminous area comprising all of the elements.

Such discs, for mounting purposes, commonly have to be provided with asheet metal housing and, for satisfactory results, it is necessary thatthe housing exclude moisture from its interior and behind the disc.Also, since disc units are commonly molded from plastic material whichis more yielding than glass, it has been a problem to apply the housingto the unit in a moisture proof manner without warping the unit andimpairing its optical properties.

Discs of the lens-reflector type commonly have their back faces silveredand moisture is particularly deleterious to such backing. This inventionpermits of dispensing with the silver on the back face and assures anhermetic seal between the housing and disc without the presence of anystrains to warp the disc.

To effect this result, this invention contemplates molding the disc inthe housing under such temperature and pressure conditions that theplastic is caused to fill the housing as the housing is being shaped tothe proper conformation. This simultaneous shaping of the housing andmolding the plastic into the housing as it is shaped, eliminates anystrains upon the disc by the housing. Also the dies or mold elementsproduce the contiguous lenticular faces on the plastic disc and axiallyaligned reflector convexities on the housing, with the result that thehousing itself serves as the reflector and dispenses with the need forsilvering.

Specifically the invention contemplates placing suitable cup shapemetallic housings in mold cavities and depositing plastic molding powderin the housings and simultaneously heating the powder to a fusingtemperature and subjecting the housing and its contents to pressurebetween properly shaped dies. The mold cavity and the dies are sodesigned that the pressure enlarges the diameter of the housing whilecrimping the edge over the plastic molded contents and forming thereflecting nodules in the bottom of the housing. The pressure isretained until the plastic has set, and if desired, the mold may beartificially cooled to expedite the setting.

A suitable apparatus for carrying out the invention is illustrated inthe drawings, in which Fig. 1 is a cross section with some of the partsin full or partial elevation, showing the mold open;

Fig. 2 is a similar view of the mold closed;

Fig. 3 is an end elevation of one of the upper dies on enlarged scale;

Fig. 4 is a sectional detail on the same scale as Fig. 3 of one of themold cavities and immediately adjacent parts, showing the mold open andthe unit parts in position, and

Fig. 5 is a similar view showing the mold closed and the unit formed.

The press elements for receiving and operating the mold may be of anystandard construction and are not shown. It will be assumed that thelower platen and the parts carried thereby are mounted on the bed of apress, and that the upper platen and parts carried thereby are fastenedto the vertically reciprocating ram of the press.

In the plane of the section of the drawings, the mold is shown as havingtwo mold cavities and a corresponding number of pairs of cooperativedies or mold inserts, but it will be understood that the mold may haveone or any greater number of cavities within practicable limits.

The upper platen I carries guide pins 2 which are long enough to remainin the bushings 3 of the guide openings in the lower platen 4 in theopen position of the mold, as shown in Fig. 1. The upper platen I alsocarries shorter guide pins 5 which are clear of the lower platen and themold plate when the mold is open, but which operate to position the moldplate, as will presently appear, and to enter the bushings 6 in guideopenings in the lower platen when the mold is closed.

The upper platen carries die members or mold inserts I and 8, and thelower platen carries respectively opposing and cooperative die members 9and [0. The mold faces of these dies have a narrow annular marginaldepressed portion H, and inside of this portion I the faces are formedinto a plurality of small contiguous spherical depressions I2. As willbe seen, the lower dies 9 and I are slightly larger in diameter than theupper dies 1 and 8, the marginal portion being that much wider in thelower dies than in the upper dies.

To attach the dies to their platens, retainer plates are used. The upperretainer plate I3 is secured to the underside of the platen l by screwsM, and the lower retainer plate I5 is secured on v the top face of theplaten 4 by screws IS. The

upper dies 1 and 8 are enlarged at their upper ends to provide ashoulder H which rests upon a corresponding retaining shoulder in theplate l3. All four of the dies shown have axial pins I8 which extendinto recesses in the retainer plates and are termed indexing pins inthat they permit the dies to be adjusted angularly so that thedepressions l2 of the upper and lower dies of each cooperative pair arein mutual opposition. Locking pins |9 are disposed so as to hold thedies in such relative angular positions.

Since the lower dies 9 and I0 rest by gravity upon the bottom retainerplate, retaining shoulders such as the shoulders I! are unnecessary andare not provided.

The mold plate which contains the mold cavities 2| and 22, rests looselyupon the retainer plate l5. The length of the lower dies 9 and I0 issuch that their molding faces are substantially flush with the retainerplate l5 and the mold cavities in the plate 23 are adapted to registerwith the lower dies. The mold cavities are bores through the mold platewhich for most of their length are of a size to receive and fit over theupper dies 1 and 8. For convenience, they may be enlarged at their upperor admission end, as shown. At their bottoms these cavities are enlargedand slightly tapered, and it is these enlarged portions 23 and 24,respectively, of the cavities 2| and 22 which, in cooperation with themold faces of the dies 9 and I0, form the final mold cavity. Guide holeswith bushings 25 are disposed and proportioned so that they receive theguide pins 5 as the mold closes and exactly locate the mold plate withthe mold cavities in register with the dies.

Coiled springs 26 depend from the retainer plate l3 and coact with themold plate 20, this plate preferably being provided with recesses 2'!disposed to receive the lower ends of the respective springs as the moldcloses. the bottoms of their recesses ahead of the entrance of the upperdies into the mold cavities, and hence the springs bear upon the moldplate during all of the molding operation and until the upper dies aresubstantially withdrawn from the lower dies and the molded units.

Each of the platens is shown as provided with two passages 28 throughwhich may be circulated means to heat and to cool the platens. Forexample, they may be connected to a steam supply to heat the dies formolding, and then to a water supply to cool the dies to accelerate thesetting of the molded unit.

In use, a metallic, cup shape member 29 of the outside diameter of theupper die and hence of the size of cavities 2| and 22, is set down ineach of these cavities as shown in Fig. 1 and the cup is then filledwith a plastic powder 30, a slight excess of the powder being provided.The cup may be of aluminum which is bright at least The springs engageon the inside so as to constitute a reflecting surface. Such a cup isadapted to serve as the housing for the finished unit.

For the purpose of piercing holes in the bottom of the reflector cup,which may be required for attachment of the unit to its support, forexample, to clothing or to a sign post, one or more pins 3| may beinserted in the lower half of the mold, one only being shown in theillustrated embodiment.

With the mold loaded as shown in Fig. 1 and the dies heated, the mold isclosed to the position shown in Fig. 2. As the dies close, the annularportions ll of dies 1 and 8 first engage the top edge of the cups 29,and either immediately, as in cavity 2|, or after perforation by theinsert or inserts 3|, as in cavity 22, the upper dies coact with theirlower dies to exert axial pressure upon the cups and their contents.This pressure causes the bottom of the cups to conform to the shape ofthe molding faces of the lower dies while imparting the shape of themolding faces of the upper dies to the plastic which has been fused bythe heat and is molded into the cup. The continued pressure causes thecups to expand into the cavity portions 23 and 24 which action crimpsthe edge of the cups inward over the margins of the units. The excessplastic will escape around the die I and if sufficient will rise intothe enlarged upper end of the cavity 2| as fiash 32.

A unitary structure consisting of the housing and plastic disc is thusmolded, and since the plastic is molded in the housing, it is free ofstrains and there is no tendency to warp. The dies are left together andare cooled by running water through the passages 28 until the moldedplastic is set. Then the ram is raised and the mold is parted, whereuponthe mold plate 20 is lifted off and unloaded. The mold is then ready torepeat the operation.

The nature of the powder used for such molding operations is well known,it being a thermoplastic, synthetic resin, of which Lucite may bementioned as an example, which when charged into a mold and subjected toheat and pressure, is changed into an infusible, rigid, molded article.

While aluminum has been mentioned as the metal of the reflector cups, itwill, of course, be understood that other metals such as nickel, forexample, may be employed. Also progress has been made in the art ofspraying or otherwise applying silver on metals, and while it iscontemplated that the aluminum or other metal, suitably polished, willsuffice as a reflector, the inner surface of the cup may be treated bysilvering to improve its reflective properties.

Due to the difference in coefficient of expansion between the plasticdisc and the metal housing, there will at atmospheric temperatures be asmall space between the side wall of the disc and the housing, which, ifpermitted to exist, would provide ingress for atmospheric moisture andcause oxidation of the reflecting surface. This invention contemplates astep which will result in the permanent sealing of the joint between theplastic and metal, and incidentally as an expedient for controlling thecolor of the reflector unit.

This step consists in introducing a proper medium to fill the space, andfor this purpose a silicon compound of the class known as silicones, andparticularly a silicone fluid of suitable viscosity is used.

The preferred method of introducing the silicone into the annular spacebetween the side wall of the plastic and its housing, is to immerse theunit just as it comes from the mold into the silicone which is reducedto a temperature at or below freezing. At the relatively hightemperature of the unit as it is removed from the mold, the plastic isexpanded and snugly fits the cup side wall. As the unit is chilled, theplastic contracts more than the metal wall, leaving a void into whichthe silicone enters, and the silicone remains as a seal in that space. Afilm of the silicone will remain on the exposed surface of the plasticand is substantially permanent since it maintains its viscosity beyondthe temperature ranges which such units encounter in use.

An incidental advantage of such use of a silicone is the fact that dyesmay be added to the silicone and reflectors of various colors be therebyobtained.

Other ways and means of carrying out the process Will occur to thoseskilled in the art, and the invention may be otherwise variouslyembodied within the scope of the following claims.

What is claimed is:

1. The method of forming auto-collimating refleeting disc units of thesinglerefracting lensrefiector type having a plurality of individuallens-reflector elements integrally joined and enclosed in a housingwithout strain upon the disc, consisting in completely filling ametallic cu with loose powdered fusiEF'tH'eYhhfifiTaTs'tifcmaterial,heating the material to a fusing temperature, axially compressing thecup and contents at said temperature betweentwodies and causing the cupto expand substantially in diameter, and restraining the upper portionof the side wall of the cup to its original size during said expansionthereby causing the said upper portion to be crimped inward over themolded plastic disc in the cup, and maintaining the pressure until thematerial is set.

2. The method as defined in claim 1 in which the axial pressure isapplied to the top edge of the cup as well as to the said material.

3. The method as defined in claim 1 in which the restraint to the sideWall of the cup is in the plane of the top surface of the finished unit.

JOHN C. HAGGART, JR.

REFERENCES CITED The following references are of record in thefile ofthis patent:

UNITED STATES PATENTS Number Name Date 304,252 Beher Aug. 26, 1884610,630 Miller Sept. 13, 1898 1,626,278 Goodman Apr. 26, 1927 1 856,415Halperin May 3, 1932 2,158,044 Haller May 9, 1939 2,260,456 Johnson Oct.28, 1941 OTHER REFERENCES Scientific American, January 1945, page M(Copy in Div. 38.)

